The invention relates generally to a cap for a container sealed by a valve. The invention more particularly relates to a cap for a container used to store pressurized materials such as a propane cylinder which stores propane under pressure. The cap allows discharge of the remaining material contained in the cylinder after the contents of the cylinder fall below a predetermined threshold.
Propane is a volatile chemical commonly used as a fuel. Propane is readily stored under pressure as a liquid. When released from pressurized storage, the liquid propane changes to a gas which may be burned in a controlled manner to provide heat and light and to satisfy other needs.
Propane is commonly stored in a metal cylinder at a pressure of approximately 150 pounds per square inch (PSI), at which pressure the propane remains in a liquid state at normal operating temperatures. Typically, the metal cylinder has a neck terminating in a mouth fitted with a check valve. The check valve may be opened to initially fill the cylinder with propane. The check valve is spring-loaded and remains closed in response to the pressure provided by the spring and the pressurized propane in the cylinder. The closed check valve retains the propane in the cylinder. The cylinder further includes a relief valve to vent propane in the event of excessive pressure.
The neck of the cylinder is adapted to be engaged by an appliance, such as a torch fixture, camp stove, lantern or the like. An appliance designed to fit the neck includes a release valve for providing controlled release of gaseous propane from the cylinder for use by the appliance. When the appliance is affixed to the cylinder, the appliance opens the check valve so that flow of gas from the cylinder is controlled by the release valve. The appliance forms a gas tight seal with the neck of the cylinder.
A user of the propane cylinder can generally determine the approximate fill level of the cylinder by lifting or shaking the cylinder. Shaking or sloshing of the liquefied propane within the cylinder provides a detectable indication that a usable amount of propane remains in the cylinder. When the cylinder is nearly empty and all of the liquefied propane has been changed to gas, the user will no longer detect the sloshing of the liquid and may determine that the cylinder is empty. When all of the contents have changed to gas, the propane cylinder may lack sufficient gas pressure to properly operate an appliance. Such empty or nearly empty cylinders are discarded by the user.
Such empty cylinders may be recycled to reclaim the metal used to fabricate the cylinder. Recycling propane cylinders is desirable to reduce the manufacturing cost of cylinders and to reduce the usage of natural resources. Recycling includes removing components such as the relief valve and the check valve and then crushing the cylinder.
Recycling or otherwise handling discarded containers used to store propane or other volatile gases can be dangerous if the discarded container retains some of the hazardous material. The mere presence of flammable material such as propane within the cylinder creates a risk of fire or explosion.
If the material within the container is under pressure, there is an additional handling risk created. For example, when recycling propane containers, current practice involves first extracting the relief valve to empty the cylinder. If the cylinder retains propane under substantial pressure, portions of the extracted relief valve may be propelled with great energy from the cylinder and create a hazard to personnel. The cylinder is more safely handled when it is empty of the volatile gas or when the gas has been discharged so that the pressure of the gas is substantially equal to atmospheric pressure. Accordingly, there is a need in the art for a device which can safely discharge a cylinder containing a pressurized fluid.
However, the discharge of the pressurized fluid from a nearly empty cylinder must be controlled. Even though a user determines that-a propane cylinder no longer contains liquid propane, the gaseous propane remaining within the cylinder may still be at pressure as great as 150 PSI. Discharge of propane at this high pressure creates a fire and handling hazard. The cylinder should not be discharged until the pressure is reduced to, for example, 60 PSI.
Accordingly, there is a further need in the art for a device which will discharge a cylinder containing a pressurized fluid only when the pressure of the fluid falls below a predetermined level.